/Engine/Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Public/PartyBeaconState.h
Update party leader for a given player with the reservation beacon (needed when party leader leaves, reservation beacon is in a temp/bad state until someone updates this)
virtual void UpdatePartyLeader ( const [FUniqueNetIdRepl](API\Runtime\Engine\GameFramework\FUniqueNetIdRepl) & InPartyMemberId, const [FUniqueNetIdRepl](API\Runtime\Engine\GameFramework\FUniqueNetIdRepl) & NewPartyLeaderId )